Recently, copying machines and printers have been used such that they are connected to a network and shared by many people to print through the network. When a printer is shared by many users, a large number of printing jobs are concentrated on a single printer. Because of this, high-speed and high reliability are required.
In addition, recently, printers have been used in various situations. Shared printers connected to a network as described above have been increasingly used, for example, in high temperature/humidity environments. Because of this, share printers are strongly required to have adaptability to high temperature/humidity environments.
Generally, to realize a toner for a high-speed operation, developability of the toner is improved by increasing the amount of an external additive. In other words, the conditions of a toner are controlled so as to easily fly. However, such a toner is vulnerable to external stress applied when the toner is stirred in a developer and when the temperature of a developer main-body increases. As a result, embedment of an external additive(s) occurs to lower durability and a toner adheres to members.
If developability is improved simply by increasing the amount of an external additive, the charge amount of toner increases with the machine time in a normal temperature and low-humidity environment (environment where an absolute content of water is low) and the problem of density reduction often occurs.
To suppress this problem, an attempt to suppress an increase in a charge amount in a normal temperature/low humidity environment has been made by adding a low-resistant particle such as a magnetic particle to a large amount of an external additive. However, if a toner is left alone in a high temperature/humidity environment, a charge amount does not quickly rise up in the beginning of a printing job and the density tends to be low.
In Patent Literature 1, a uniform chargeability is obtained by adding a magnetic particle as an external additive to silica. Owing to this, a certain effect is produced against scattering of a toner in a developer. However, if the use as mentioned above is presumed, it is difficult to satisfy an initial density after a toner is left alone in a high temperature/humidity environment and long-term stability in a high-speed printing system at the same time. Because of this, there is room for improvement.
In Patent Literature 2, a development/transfer step is stabilized by controlling the total coverage of toner-core particles with an external additive. Indeed, a certain effect is produced on predetermined toner core particles by controlling a calculated theoretical coverage. However, if the use as mentioned above is presumed, it is difficult to satisfy an initial density after a toner is left alone in a high temperature/humidity environment and long-term stability in a high-speed printing system at the same time. Because of this, there is room for improvement.
Furthermore, Patent Literatures 3 and 4 propose that long-term stability is improved by adding a spacer, thereby suppressing embedding of an external additive. Also, in this case, it is difficult to satisfy an initial density after a toner is left alone in a high temperature/humidity environment and long-term stability in a high-speed printing system at the same time. Because of this, there is room for improvement.
As mentioned above, it is required to develop a toner having an initial density satisfying quality even in a high temperature/humidity environment and having excellent durability in a high-speed printing system; however, there are a great many technical problems at present. Because of this, there is room for improvement.